Funky Prints

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I recently moved to Cura, and I had to do some recalibration of the Ultimaker as it was jamming frequently.

I finally got it to print tonight, after I did the following:

1. Core out the end of the bowen tube in contact with the nozzle assembly with a drill to make the exit aperture wider

2. Readjusted the extruder screw tightness very carefully

3. Moved printing temperature from 185C (on Netfabb) to 220C (on Cura, since I was printing at high speed)

So it was printing all fine, though at a higher temperature so now I could smell the plastic, and its appearance was more fluid and wet-like. And I was pretty glad that I improved the accuracy of the steppers by tightening all the belts and rods properly. So surface finish was awesome.

But then what happened was that mid-way the filament began to jam again, I could tell by listening to the extruder motor grind away. So not wanting to lose my print, I heroically fed the printer with my hands, hoping brute strength could bypass the bad section of filament. And it worked! After a while the extruder began to pick up and filament came out smoothly from the nozzle again.

I'm not sure why this happened, that's why I'm posting this. All my adjustments seem to work alright at least for the first 50% of the print and the last 40%. So I'm wondering if what happened was the following:

1. The diameter of PLA filament is inconsistent

2. PLA plastic contains impurities

I believe that: Either of the two issues will cause the melting rate of the filament to change, which would cause the extruder to slow down its rate of extrusion (or speed up, but most likely slow down in my case). When the rate of extrusion slows, the soft melty filament expands under pressure from the extruder motor to fill up the Bowen Tube. When this happens, the soft melty filament comes into contact with the cool wall of the Bowen Tube and hardens as it looses heat to the wall. This hardening action thus causes the jam.

I was also studying the designs of the Reprap and I notice they place the extruder motor directly on top of the nozzle assembly. Perhaps if we shortened the melt zone of the Ultimaker and do away with the Bowen Tube, we could get more reliable prints? I really dislike the design of the PEEK-Bowen Tube interface, practically all my jams happen there. There must be a better way of feeding filament into the nozzle, whilst reducing the length of the melt zone at the same time - since I believe I have a long melt zone extending from the PEEK to about 1cm upwards into the Bowen Tube.

Here's a photo to see the result! It did complete printing by the way! =D So I am not totally upset lol!

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Okay to be scientific, I printed a second cube and watched it very carefully.

What happened was that the filament began to jam again. In total the filament jammed 4 times, as seen by the 3 distinct lines along the sides of the cube, as well as the gaps at the top of the cube. As I was watching it print, I counteracted jamming successfully by using my hand to apply force to the filament being fed into the extruder motor. My new theory could be that the toothed gear of the extruder motor is getting dirty and loosing grip.

As jamming occurred randomly, it cannot be attributed to some sort of systematic error, which makes diagnosis tougher.

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Check and make sure your hobbed bolt is clean. The knurling on top of the threads creates hooks that trap material very effectively. I use an x-acto knife to clean it out before any print longer than say 3 hours.

Measure the filament diameter with a digital caliper several times over a meter. does the diameter change? That will cause the extruder to skip as well.

Don't over tighten the thumb screw. If you do, the filament will deform and get wedged in the bowden. If you have trouble pushing or pulling the filament without the nozzle on, that's why. You can add an extra M3 nut as a jam nut to keep it from changing on you. For reference, the head of my thumb screw is 3.62mm from the wood.

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Ultimaker should just recommend Cura for beginners rather than Netfabb or RepG which both are so buggy.

There is a long list of "recommendations" that I am supposed to look into. Besides the ones you mentioned, there is Kisslicer, sendG, and a whole bunch of others... However when there are problems, you need to have a person in support that can quickly determine if its a bug or something that the user is doing wrong and knows the behavior of the software, instead of sending them back to the forums while saying "Get your help there".

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Ultimaker should just recommend Cura for beginners rather than Netfabb or RepG which both are so buggy.

There is a long list of "recommendations" that I am supposed to look into. Besides the ones you mentioned, there is Kisslicer, sendG, and a whole bunch of others... However when there are problems, you need to have a person in support that can quickly determine if its a bug or something that the user is doing wrong and knows the behavior of the software, instead of sending them back to the forums while saying "Get your help there".

Kisslicer is none-free.

SendG is very basic, and I don't think it works any better then printrun. Also, due do it's C# nature, it's harder to get working on all different platforms.

While Cura is pretty nice, it has it's own share of bugs. And it's quite new. Ultimaker choose to support ReplicatorG, and they currently stick with what they know. Which is very understandable.

You also have to understand that Cura is less then 3 months old. Cura is newer then the Ultimaker, so they did not have this option when they started. Cura started out of frustration with Skeinforge and ReplicatorG. So it's not that odd that is has improvements over it at some points. But Cura is currently also going trough rapid development cycles. Lots of stuff can be changed from week to week, that's not easy to support.